An immobilized enzyme is an enzyme that is attached to an insoluble material, which allows enzymes to be held in place throughout a reaction, separated from the products after the reaction, and used again if desired. There are three general methods for immobilizing an enzyme in an IMER. The first general method includes adsorption on glass, alginate beads or matrix, in which the enzyme is attached to the outside of an inert material. As adsorption is not a chemical reaction, the active site of the immobilized enzyme may be blocked by the matrix or bead, reducing the activity of the enzyme. The second general method includes entrapment, in which the enzyme is trapped in insoluble beads or microspheres, such as calcium alginate beads. However, the insoluble substance can hinder the arrival of reactants and the exit of products. The third general method is cross-linkage, in which the enzyme is covalently bonded to a matrix through a chemical reaction.
Covalently-linked IMERs and IMER media are available in various forms. For example, POROSZYME media, available from APPLIED BIOSYSTEMS (California, USA), employ polystyrenedivinylbenzene particles. STYROSZYME™ media, available from OraChrom, Inc. (Massachusetts, USA), employs fully pervious poly(styrene-divinylbenzene) matrices. Agarose bead media is also available from Thermo Fisher Scientific Inc (Massachusetts, USA). Presently, most commercial IMERs use these media under low pressure conditions.